Light-emitting diode (LED) arrays are used in non-impact printers for recording or printing an image on a photosensitive medium such as film or paper. The LEDs are arranged in a linear array and a relative movement is made between the linear array and the photosensitive medium to produce a scanning movement of the linear array over the surface of the photosensitive medium. The photosensitive medium is exposed to provide a desired image a line at a time as it is advanced relative to the LED array. Each LED in the array exposes a pixel in the photosensitive medium with electronic signal information from a source that defines an image. Image processing electronics converts the information into electrical current.
In a printing system, such as that described in U.S. Pat. No. 6,061,078, control characters are sent across a communication channel to designate the starting point of a line of image data, the ending point of the line of data, and the time to start an exposure sequence. In the system described in U.S. Pat. No. 6,061,078, the same control character is used to designate the end of the line of data as to designate the start of the line of data. A separate control character is used to designate the start of the exposure sequence.
These control characters are sent with each line of image data. The line of image data that is exposed onto the photoconductor is the line of data that was sent previously. Basically, the imaging element has a one line buffer that holds the ‘just sent’ line of data and then exposes the line of data that was sent on the prior transmission interval.
The photoconductor is a drum or web that is moving at a nominal rate. Signals are sent from electronics associated with the photoconductor that indicate when the current line of data should be imaged onto the photoconductor. The transmitter accesses these signals and determines when to send the next line of data to the receiver. In each case, the transmitter sends a start of line character (SOL), the image data, an end of line character (EOL), and then the exposure start character (EXP). For the system described in U.S. Pat. No. 6,061,078, the SOL character and the EOL character have the same bit pattern.
In a printing system, as described in U.S. Pat. No. 6,061,078, there are many noise sources. The equipment, in general, requires high voltage power supplies and charging elements. There are many opportunities for arcing to occur, which generates a broadband of spurious noise. In this environment, the opportunity exists for these external noise sources to interfere or corrupt the communication channel. Since the transmission of data across the link is tied to the movement of the photoconductor, the data must be present at the imaging element when the exposure sequence starts. If erroneous data is stored at the imaging element when the exposure sequence starts, a corrupted image will be produced. Specifically, the integrity and timing of the control characters must be maintained since a loss of a single control character interrupts the synchronization between the transmitter and receiver. The resulting image produced at the photoconductor will be corrupted until the transmitter and receiver can regain synchronization.